Phosphatidylethanolamide derivatives of prostaglandins E1 and E2

Prostaglandins E₁ (PGE₁) and E₂ (PGE₂) have been coupled with the amine group of phosphatidylethanolamine (PE) by means of dicyclohexylcarbodiimide. These complexes basically mimic the relaxant and contractile effects of the corresponding free prostaglandins (PGs) on various smooth muscle preparations, but exhibit a delayed onset of action and a lower affinity for the PG receptors. The complexes are comparable with the free, parent PGs, in their intrinsic activities. The same holds true for the effects on blood pressure and on the motility of the uterus . The PGE₂-PE complex is hydrolysed to release obviously free PGE₂ by cell-free homogenates prepared from various tissues, but not by blood plasma. The PGE₂-PE complex is immunologically indistinguishable from the free PGE₂.     

Prostaglandin E2 and muscle protein turnover inPseudomonas aeruginosa sepsis

Rats were injected intraperitoneally withPseudomonas aeruginosa (septic group) or sterile 0.9% NaCl (controls). Soleus muscles were excised 7 h later, and muscle prostaglandin E₂ release and tyrosine release were measured in vitro. Muscles of septic rats exhibited 226–326% higher release of prostaglandin E₂ and 54–84% higher net proteolysis than muscles of controls. Inclusion of aspirin or indomethacin in the incubation medium almost completely inhibited prostaglandin E₂ production, but had no effect on net proteolysis in muscles from either group. Inclusion of cycloheximide, a protein synthesis inhibitor, increased tyrosine release of control muscles by 42%, whereas no statistically significant increase was observed in muscles from infected rats. However, total proteolytic rate, indexed by tyrosine release in the presence of cycloheximide, was 22% higher in muscles of septic rats compared to that of control animals. Concomitantly, inclusion of cycloheximide inhibited prostaglandin E₂ release by muscles of infected rats by 91% and that of controls by 65%. It is concluded that (a) muscles of septic animals exhibit a pronounced stimulation of prostaglandin E₂ release and net proteolysis, combined with a small increase in total proteolytic rate, (b) the stimulation of net proteolysis is mainly due to inhibition of protein synthesis, (c) the increases in net and total proteolysis appear to be independent of prostaglandin E₂ production, (d) cycloheximide has a previously unrecognized inhibitory effect on muscle prostaglandin E₂ production.     

Prostaglandins and renin release: III. Effects of PGE1, E2 F2α and D2 on renin release from rabbit renal cortical slices

We have investigated the direct effects of prostaglandins E₁, E₂, F_2α and D₂ on renin release from rabbit renal cortical slices. Prostaglandin E₁ (PGE₁) was the most potent stimulant of renin release, while PGE₂ was 20–30 fold less active. PGF_2α was found not to be an inhibitor of renin release as reported by others, but rather a weak agonist. PGD₂ up to a concentration of 10 μg/ml had no activity in this system. That the stimulation of renin release by PGE₁ is a direct effect is supported by the finding that PGE₁-induced release is not blocked by L-propranolol or by Δ^5,8,11,14-eicosatetraynoic acid (ETYA), a prostaglandin synthesis is inhibitor. The fatty acid precursor of PGE₁, Δ^8,11,14-eicosatrienoic acid, also stimulated renin release, an effect which was blocked by ETYA. In addition to the above findings, ethanol, a compound frequently used to dissolve prostaglandins, was shown to inhibit renin release.     

Failure of prostaglandins E1 and E2 to alter canine gastric mucosal cyclic nucleotides

The action of prostaglandins and indomethacin on gastric mucosal cyclic nucleotide concentrations was evaluated in 18 anesthetized mongrel dogs. Prostaglandins E₁ (PGE₁) and E₂ (PGE₂) (25 μg/kg bolus, then 2 μg/kg/min) were administered both intravenously (4 experiments; femoral vein) and directly into the gastric mucosal circulation (10 experiments; superior mesenteric artery). The possible synergistic effect of pre-treatment and continuous arterial infusion of indomethacin (5 mg/kg bolus for 5 min, then 5 mg/min), a prostaglandin synthetase inhibitor, with PGE₂ was studied in 4 experiments. Antral and fundic mucosa were biopsied and measured by radioimmunoassay for cyclic nucleotides. Doses of PGE₁ and PGE₂ which inhibited histamine-stimulated canine gastric acid secretion did not significantly alter antral or fundic mucosal cyclic nucleotide concentrations. Concomitant infusion of PGE₂ with indomethacin did not potentiate the mucosal nucleotide response compared to PGE₂ alone. These studies fail to implicate cyclic nucleotides as mediators of the inhibitory acid response induced by PGE₁ or PGE₂ in intact dog stomach.     

Effect of prostaglandins E1, E2 and F2α on neutrophil aggregation

Recently we have found that chemotactic factors stimulate neutrophils in suspension to aggregate. Because of an obvious analogy to platelet aggregation, we examined the influence of three prostaglandins on this process. Prostaglandins E₁, E₂ and F_2α alone did not cause aggregation of the neutrophils but were able to partially inhibit the aggregation response induced by the synthetic chemotactic tripeptide, formly-methionyl-leucyl-phenylalanine. The minimal inhibitory concentrations for prostaglandins E₁, E₂ and F_2α were 10⁻⁷, 10⁻⁶ and 10⁻⁵M, respectively. These results are similar to those found for the prostaglandin-induced inhibition of platelet aggregation. It may be, therefore, that neutrophil aggregation, like platelet aggregation, is modulated by intracellular prostaglandins and other products of arachidonic acid metabolism.     

UP-regulaton of prostaglandin E2 binding and of prostanoid release in rabbits producing antibodies

German Giant rabbits successfully immunized agianst prostaglandin (PG) E₂ as shown by a rise in antibody titers developed gastric mucosal lesions. Enzymatically dispersed gatric mucosal cells of these animals had a significantly enhanced production of PG₂ and PG I₂ as measured by specific radioimmunoassays. This may be explained by an increased supply with endogenous arachidonic acid (as indicated by an enhanced phospholipase A₂/LAT ratio) and by a higher activity of the subsequent PG forming enzymes (as indicated by a more effectvie stimulation of PG production by exogenous arachidonic acid). Gastric mucosal plasma membranes of immunized rabbits had significantly high PG E₂ binding capacity (108 ± 9 fmol/mg protein) than those of nomimmunized rabbits (72 ± 5 fmol/mg protein). The ligand affinity was not afected by immunization. Neither histamine-stimulated ¹⁴C-aminopyrine uptake of isolated parietal cells as a marker for acid production nor its inhibition by PG E₂ were influenced by receptor up-regulation. The increased eicosanoid release can be regarded as an endogenous defense emchanism against increased mucosal vulnerability caused by PG E₂ scavenging. The potential role of PG E₂ receptor up-regullation in support of this process remains to be established.     

Specific prostaglandine E1 and A1 binding sites in rat a dipocyte plasma membranes

Rat adipocyte plasma membranes sacs have been shown to be a sensitive and specific system for studying prostaglandin binding. The binding of prostaglandin E₁ and prostaglandin A₁ increases linearly with increasing protein concentration, and is a temperature-sensitive process. Prostaglandin E₁ binding is not ion dependent, but is enhanced by GTP. Prostaglandin A₁ binding is stimulated by ions, but is not affected by GTP.Discrete binding sites for prostaglandin E₁ and A₁ were found. Scatchard plot analysis showed that the binding of both prostaglandins was biphasic, indicating two types of binding sites. Prostaglandin E₁ had association constants of 4.9 · 10⁹ 1/mole and 4 · 10⁸ 1/mole, while the prostaglandin A₁ association constants and binding capacities varied according to the ionic composition of the buffer. In Tris-HCl buffer, the prostaglandin A₁ association constants were 8.3 · 10⁸ 1/mole and 5.7 · 10⁷ 1/mole, while in the Krebs—Ringer Tris buffer, the results were 1.2 · 10⁹ 1/mole and 8.6 · 10⁶ 1/mole.Some cross-reactivity between prostaglandin E₁ and A₁ was found for their respective binding sites. Using Scatchard plot analysis, it was found that a 10-fold excess of prostaglandin E₁ inhibited prostaglandin A₁ binding by 1–20% depending upon the concentration of prostaglandin A₁ used. Prostaglandin E₁ competes primarily for the A prostaglandin high-affinity binding site. Similar Scatchard analysis using a 20-fold excess of prostaglandin A₁ inhibited prostaglandin E₁ binding by 10–40%. Prostaglandin A₁ was found to compete primarily for the E prostaglandin low-affinity receptor.All of the bound [³H]prostaglandin E₁, but only 64% of the bound [³H]-prostaglandin A₁ can be recovered unmetabolized from the fat cell membrane. There is no non-specific binding of prostaglandin E₁, but 10–15% of prostaglandin A₁ binding to adipocyte membranes is non-specific. Using a parallel line assay to measure relative affinities for the E binding site, prostaglandin E₁ > prostaglandin A₂ > prostaglandin F_2α. Prostaglandin E₂ and 16,16-dimethyl prostaglandin E₂ were equipotent with prostaglandin E₁, while other prostaglandins had lower relative affinities. 7-Oxa-13-prostynoic acid does not appear to antagonize prostaglandin activity in adipocytes at the level of the receptor.     

Enterohepatic circulation of N-acetyl-leukotriene E4

N-Acetyl-leukotriene E₄, the end product of leukotriene C₄ metabolism in the mercapturic acid pathway, was rapidly eliminated from the blood circulation into the bile of rats. Part of the N-acethyl-leukotriene E₄ secreted from bile into the intestine undewent enterohepatic circulation. Leukotriene absorption occurred from the small intestine and from the colon. Biliary and urinary excretion within 5.5 h amounted to 15 and 2%, respectively, of the intraduodenally administered N-acetyl- H leukotriene E₄ in animals anesthetized with ketamine. HPLC analyses indicated that 35% of the biliary radioactivity corresponded to unchanged N-acetyl- H leukotriene E₄, while 65% in bile and 100% in urine were polar metabolites. Enterohepatic circulation extends the biological half-life of N-acetyl-leukotriene E₄.     

Prostaglandins E1 and E2 stimulate the proliferation of pulmonary artery smooth muscle cells

Prostaglandins E₁ and E₂ are thought to be inhibitors of the growth of systemic vascular smooth muscle cells (SMC). However, their effect on the proliferation of SMC from the pulmonary artery (PA) has not been described and was the subject of this investigation. Cultures of bovine PA SMC were exposed to PGE₁ and PGE₂ under various conditions and their growth was assessed. PGE₁ and PGE₂ did not inhibit the growth of PA SMC in 10% fetal calf serum (FCS), but instead caused a dose dependent (10 ng - 1 μg/ml) increase in [³H]-thymidine incorporation when added to cultures containing 0.5% FCS; the highest doses resulted in 95% and 75% increases in [³H]-thymidine uptake at 24 hours with PGE₁ and PGE₂ respectively. This was accompanied by a modest increase in actual cell numbers (e.g., 20% with 1 μg/ml PGE₁). Furthermore, PGE₁ could mimic insulin-like growth factor (IGF-1) by potentiating the stimulation of SMC growth by fibroblast growth factor, suggesting that PGE₁ may act as a progression factor in the growth cycle of these cells. There was, however, no effect of PGE₁ on the proliferation of bovine aortic SMC. We conclude that, contrary to most reported effects on systemic SMC, PGE₁ and PGE₂ do not inhibit the proliferation of PA SMC but rather stimulate it.     

Prostaglandin E1 decreases circulating endothelial cells

Prostaglandin E₁ (PGE₁) has been claimed to have cytoprotective effects and also to decrease thrombogenicity. The effect of intraarterial (i.a.) and intravenous (i.v.) administration of PGE₁ on the number of circulating endothelial cells (CEC) was investigated in patients with peripheral vascular disease (PVD). Patients with hyperlipoproteinemia and also smokers exhibited higher numbers of CEC. PGE₁ significantly (p < 0.01) decreased CEC. In parallel, plate let survival was prolonged (r = −0.82). This effect lasted for more than a month after stopping PGE₁-therapy. The observed decrease in CEC reflects the decreased thrombogenicity and improved haemostasis achieved after PGE₁.     

Separation and quntification of prostaglandins E1 and E2 as their panacyl derivatives using reverse phase high pressure liquid chromatography

Separation and quatification of prostaglandin E₁ (PGE₁) and prostaglandin E₂ (PGE₂) were achieved using reverse phase high performance liquid chromatography (HPLC). Panacyl bromide (p-(9-anthroyloxy)phenacyl bromide) (PAB) derivatives of PGE₂ and PGE₁ were prepared. Reverse phase HPLC using a linear gradient of 56% to 80% acetonitrile in water containing 0.10% acetic acid gave baseline resolution of the two derivatives. A 3 um diameter particle, C18 column provided good resolution and reproducible recoveries. Human synovial tissue cells were incubated with the precursor fatty acids for PGE₁ or PGE₂ and stimulated with a crude Interleukin 1 (IL-1) preparation. Cells grown in the presence of dihomogammalinolenic acid (DGLA), the precursor for PGE₁, made significantly more PGE₁ than cells grown in control medium or in the presence of arachidonic acid, precursor for PGE₂. PGE₂ synthesis was reduced when DGLA was added to cells (resting or IL-1-stimulated).     

Interactions of prostaglandins with subpopulations of ovine luteal cells. I. Stimulatory effects of prostaglandins E1, E2 and I2

Preparations of small and large steroidogenic cells from enzymatically dispersed ovine corpora lutea were utilized to study the effects of luteinizing hormone (LH) and prostaglandins (PG) E₁, E₂ and I₂. Cells were allowed to attach to culture dishes overnight and were incubated with either LH (100 ng/ml), PGE₂, PGE₂, or PGI₂ (250 ng/ml each). The secretion of progesterone by large cells was stimulated by all prostaglandins tested (P < 0.05) while the moderate stimulation observed after LH treatment was attributable to contamination of the large cell population with small cells. Prostaglandins E₁ and E₂ had no effect on progesterone secretion by small cells, while LH was stimulatory at all times (0.5 to 4 hr) and PGI₂ was stimulatory by 4 hr. Additional studies were conducted to determine if the effects of PGE₂ upon steroidogenesis in large cells were correlated with stimulated activity of adenylate cyclase. In both plated and suspended cells PGE₂ caused an increase (P < 0.05) in the rate of progesterone secretion but had no effect upon the activity of adenylate cyclase or cAMP concentrations within cells or in the incubation media. Exposure of luteal cells to forskolin, a nonhormonal stimulator of adenylate cyclase, resulted in marked increases in all parameters of cyclase activity but had no effect on progesterone secretion. These data suggest that the actions of prostaglandins E₁, E₂ and I₂ are directed primarily toward the large cells of the ovine corpus luteum and cast doubt upon the role of adenylate cyclase as the sole intermediary in regulation of progesterone secretion in this cell type.     

Effects of prostaglandins E1 and E2 on activity in laryngeal and pharyngeal afferent fibers

Prostaglandins (PG) E₁ and E₂ were applied topically to the receptive fields of feline laryngeal and pharyngeal sensory receptors, while action potentials were recorded from single - or few-fiber preparations of the superior laryngeal nerve. When initially dissolved in ethanol, PGs stimulated these sensory receptors. If ethanol was not used as a solvent for the PGs, they did not stimulate the sensory receptors. Similarly, local application of dilute (0.025%, v/v) solutions of ethanol alone excited the receptors, whereas phosphate buffer alone did not. Thus PGE₁ and PGE₂ do not themselves stimulate sensory receptors in the larynx and pharynx. These findings suggest that irritant properties of PGEs on upper airways are attributable to the ethanol used as a solvent.     

Stimulatory effects of prostaglandin E1 on rat anterior pituitary cyclic amp and luteinizing hormone release

The effect of prostaglandin E₁ (PGE₁) on rat anterior pituitary cyclic AMP accumulation and luteinizing hormone (LH) release was studied both in vivo and in vitro. Addition of PGE₁ to incubation medium over a concentration range of 10^-6 to 10^-4 M produced a graded increase in pituitary cyclic AMP. At the lowest concentration (10^-6 M) there was no significant increase in LH release, but proportional increments in LH release were seen with increasing concentrations of PGE₁.Ten minutes after intravenous administration of 5 μg of PGE₁ to adult male rats, pituitary cyclic AMP was substantially increased while serum LH levels were not changed. Administration of a higher dose of PGE₁ (20 μg) produced a greater increase in pituitary cyclic AMP; and, at this dose serum LH was significantly increased. These results suggest that the PGE₁ effect on LH release is mediated by the adenyl cyclase — cyclic AMP system.     

Neurological and electroencephalographic changes in newborns treated with prostaglandins E2 and E2

Six newborns with obstructive right heart lesions were examined neurologically and electroencephalographically during treatment with prostaglandin (PG) E₁ or E₂ given to maintain patency of the ductus arteriosus and to increase pulmonary blood flow. PG was administered intravenously or intraarterially in the aortic isthmus proximal to the ductus arteriosus. Besides a rise in arterial oxygen saturation, all patients had some sign of central nervous system involvement. The electroencephalogram showed minor changes suggestive of sedation. In addition, three patients in whom PG given intravenously presented various combinations of neurological abnormalities (“myoclonic jerks”, apnoeic spells, hiccup) of subcortical origin. Side-effects subsided after stopping the treatment anf posed no problem in the management of the patients. These findings confirm the usefulness and safety of the PG therapy and indicate that the intraaortic route of administration is preferable.     

Prostaglandin E1 metabolism by human plasma

An enzymic prostaglandin E₁ metabolising system in human plasma is described. Various properties of the system have been investigated. Metabolism of prostaglandin E₁ added to whole human blood or plasma, particularly in low concentrations such as those found physiologically, can be extremely rapid and extensive. The importance of these findings in relation to the extraction of prostaglandins from human blood or plasma is discussed.     

Mechanism of increased renal prostaglandin E2 in uranyl nitrate-induced acute renal failure

We have previously demonstrated that decreased cortical prostaglandin metabolism can contribute significantly to an increase in renal tissue levels and activity of prostaglandin E₂ in bilateral ureteral obstruction, a model of acute renal failure. In the present study, we have further investigated whether alterations in prostaglandin metabolism can occur in a nephrotoxic model of acute renal failure. Prostaglandin synthesis, prostaglandin E₂ metabolism (measured as both prostaglandin E₂-9-ketoreductase and prostaglandin E₂-15-hydroxydehydrogenase activity), and tissue concentration of prostaglandin E₂ were determined in rabbit kidneys following an intravenous administration of uranyl nitrate (5 mg/kg). No changes in the rates of cortical microsomal prostaglandin E₂ and prostaglandin F_2α synthesis were noted at the end of 1 and 3 days, while medullary synthesis of prostaglandin E₂ fell by 47% after 1 day and 43% after 3 days. Cortical cytosolic prostaglandin E₂-9-ketoreductase activity was found to be decreased by 36% and 76% after 1 and 3 days respectively. No significant changes were noted in cortical cytosolic prostaglandin E₂-15-hydroxydehydrogenase activity after 3 days. Cortical tissue levels of prostaglandin E₂ increased by 500% at the end of 3 days. These data demonstrate that in nephrotoxic acute renal failure, decreased prostaglandin metabolism (i.e., prostaglandin E₂-9-ketoreductase activity) can result in increased tissue levels of prostaglandin E₂ in the absence of increased prostaglandin synthesis and suggest that alterations in prostaglandin metabolism may be an important regulator of prostaglandin activity in acute renal failure.     

Effect of angiotensin II and norepinephrine on release of prostaglandins E2 and I2 by the perfused rat mesenteric artery

Prostaglandin E₂ (PGE₂) and 6 keto-PGF_1α, the stable metabolite of prostacyclin (PGI₂), have been measured in the effluent of perfused rat mesenteric arteries by the use of a sensitive and specific radioimmunoadday (RIA) method. The PGE₂ and 6-keto-PGF_1α were continuousyl released by the unstimulated mesenteric artery over a period of 145 min. After 100 min of perfusion the release of PGE₂ and 6-keto-PGF_1α was 4.5 ± 8.4 pg/min and 254 ± 75 pg.min respectively, which is in accord with the general belief that PGI₂ is the major PG synthesized by arterial tissue. Angiotensin II (AII) 5 ng/ml) induced an increased of PGE₂ and 6-keto-PGF_1α release without changing the perfusion pressure. The effect of norepinephrine (NE) injections on release of PGs depended on the duration of the stabilization period. The changes of perfusion pressure induced by NE were not related to changes in release of PGs. Thus, it seems that the increase of PG release induced by AII and NE was due to a direct effect of the drugs on the vascular wall. This may represent an important modulating mechanism in the regulation of vascular tone.     

Inhibitors of protein synthesis,puromycin and emetine,inhibit prostaglandin E2 release by skeletal muscle

Addition of 1μM puromycin or 1 μM emetine to rat soleus muscle in vitro decreases muscle prostaglandin E₂ release by 51–77%. This inhibition appears to be caused by decreased availability of endogenous arachidonic acid for prostaglandin E₂ synthesis, because neither puromycin nor emetine inhibits muscle prostaglandin E₂ production from arachidonic acid added into the incubation medium.